Colorimeter, infrared

The absorption spectroscopy has been widely used for monitoring the rate of chemical reactions. During the reaction, if there is either appearance of colour in a colourless solution or disappearance of colour in a coloured solution or a species which absorbed at a specific wavelength is formed, the spectroscopic technique can be used. Instruments like colorimeters and spectrophotometers are available to cover the visible, near infrared and ultra violet region of the spectrum (200-1000 nm). The absorption spectroscopy is governed by well-known Beer-Lambert s Law according to which ... 

It has proven feasible to take the electrical output from photocells or phototubes and either with or without amplification record the magnitude and duration of the output. The recording may be made either in the form of a line tracing on a moving chart or may be converted to numerical values and printed by a read-out device. Further refinements can be supplied in which the instrument converts optical densities (or transmittance units) to concentration values. More intricate recording colorimeters or spectrophotometers are also available for continuous scanning and recording of complete spectra from ultraviolet to infrared. No further discussion of these will be attempted since they do not serve a normal function in routine clinical chemistry laboratories. 

The limitations of early instrumentation were extreme. Engineers were first able to get on-line measurements for only the simplest process parameters - initially only temperature and pressure. As interest in on-line measurements grew, various manufacturers developed instrumentation for chemical process streams. Soon, instrumentation was available for simple infrared measurements, water determination, simple ultraviolet measurements, density, and viscosity. The spectroscopic instruments (1R, UV, etc) of this era were simplistic devices similar to colorimeters that used filters to provide the appropriate frequency or range of frequencies to quantitate one or more components of the process stream. 

We use the term colorimeter to designate an instrument for absorption measurements in which the human eye serves as the detector using one or more color-comparison standards. A photometer consists of a source, a filler, and a photoelectric transducer as well as a signal processor and readout. Note that some scientists and instrument manufacturers refer to photometers as colorimeters or photoelectric colorimeters. Filter photometers are commercially available for absorption measurements in the ultraviolet, visible, and infrared regions, as well as emission and fluorescence in the first two wavelength regions. Photometers designed for fluorescence measurements arc also called fluorometers. 

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